Vehicle occupant protection systems that have at least one actuatable protection device are known in the art. An actuatable protection device of such a system is actuated upon the occurrence of a condition for which a vehicle occupant is to be protected. Two examples of conditions for which a vehicle occupant is to be protected are the occurrence of a vehicle frontal collision and the occurrence of a vehicle side collision.
One type of actuatable protection system includes an air bag module mounted within a vehicle such that an air bag of the module is inflatable within an occupant compartment of the vehicle. The air bag is inflated upon the occurrence of a condition, such as a vehicle frontal collision. Another type of actuatable protection system includes a side curtain module mounted within a vehicle such that an inflatable side curtain of the module is extendible between an occupant and side structure (e.g., door glass) of a vehicle. The side curtain is extended upon the occurrence of a condition, such as a vehicle side collision.
Typically, a protection system includes a controller that controls actuation of the one or more protection devices within the system. The control provided by the controller is in response to one or more signals provided from one or more crash sensors, or the processing of the one or more signals. For example, the protection system may include an accelerometer that outputs a signal indicative of vehicle crash acceleration. The controller determines whether the signal is indicative of crash acceleration above a predetermined threshold. When the threshold is exceeded, the controller actuates one or more protection devices.
Many known systems utilize sensory input from two sensors and/or the processing of the two sensory inputs in somewhat of a redundant fashion to make a final determination regarding actuation of a protection device. Both sensory inputs must indicate, or result in determinations, that a crash condition is present in order for actuation to occur. Typically, the redundant aspect is referred to as providing a "safing" function. Within a system that has a safing arrangement, one sensor/processing arrangement is referred to as primary and the other sensor/processing arrangement is referred to safing.
One example of a system that includes a safing function is a system that has an accelerometer responsive to a crash acceleration (e.g., deceleration along a longitudinal axis of a vehicle) and a simple mechanical switch that is responsive to crash acceleration in the same direction (e.g., longitudinal). The output of the accelerometer is processed to determine if a threshold value is exceeded. The mechanical switch merely closes in response to sufficient vehicle deceleration. Typically, the mechanical switch closes at a relatively low crash acceleration value compared to the threshold value utilized in conjunction with the accelerometer output. Accordingly, the switch closes at a very early stage of a vehicle crash. With the switch closed, when the crash acceleration as perceived by the accelerometer exceeds the predetermined threshold value, an occupant protection device is actuated.
As sophistication of occupant protection systems continue to increase, the number of protection system devices, the number of sensory inputs, and the amount of sensory data to process continues to increase.